This invention relates to a control device for controlling an output from a generator, and more particularly to such a device for controlling a rectified output from an AC generator in accordance with a temperature.
For example, motor vehicles comprise the internal combustion engine, the AC generator driven by the internal combustion engine, and the battery charged with a rectified output from the AC generator. In order to control the rectified output to a predetermined magnitude, a voltage regulator is disposed within the AC generator or on an enclosure thereof and includes a pair of output transistors put in a Darlington configuration and connected at one end to one portion of the rectified output through a field coil disposed on the AC generator and at the other end to ground, a control transistor connected to a base circuit of the output transistors, and a Zener diode connected to the control transistor. The Zener diode has been previously connected to both a first junction of a pair of resistors (which form a first voltage dividing circuit connected across the one portion of the rectified output) and a second junction of a resistor and a thermally sensitive switch element (which form a second voltage dividing circuit connected across the one portion of the rectified output) through respective diodes forming an "OR" circuit. The thermally sensitive switch element is connected to ground and responsive to a predetermined temperature to abruptly increase in resistance in a positive direction.
When the rectified output increases to raise a potential at the first junction to a predetermined magnitude, the Zener diode is turned on to turn the output transistors off through the turn-on of the control transistor resulting in the interruption of a field current flowing through the field coil. Thus the rectified output from the AC generator decreases to reduce the potential at the first junction to be less than the predetermined magnitude. At that time, the Zener diode is turned off to turn the output transistors on. The process as described above is repeated to maintain the rectified output from the AC generator to the predetermined magnitude.
Also the ambient temperature for the AC generator may abruptly increase for some reasons. With the AC generator operated under high electrical loading, the ambient temperature tends to reach a high magnitude at and above which the AC generator will be thermally broken or extremely decrease in lifetime with heat generated by the same itself. This is attended with a corresponding increase in temperature of the thermally sensitive switch element. Thus the thermally sensitive switch element exceeds the predetermined temperature set therefor to have a magnitude of resistance abruptly increased in the positive direction resulting in an increase in potential at the second junction. This causes the Zener diode to be turned on through the diode connected to that junction regardless of the potential at the first junction. Therefore no field current flows through the field coil as described above. Thus the AC generator does not generate the output and hence heat. Accordingly the ambient temperature abruptly decrease until the potential at the second junction decreases due to the temperature of the thermally sensitive switch element is less than the predetermined one and becomes independent of the operation. Thereafter the Zener diode and the control transistor continue to be operated under the control of the potential at the first junction.
In the conventional voltage regulator as described above, the potential at the first junction is connected to that at the second junction, through the "OR" circuit. Thus a reference voltage set by the Zener diode has a forward voltage drop across the diode in the "OR" circuit serially inserted thereinto. Accordingly the conventional voltage regulator not requiring a temperature gradient should avoid the influence of a negative temperature coefficient of the forward voltage drop on a temperature rise. The negative temperature coefficient is of about 2 mV/C.degree..
As a result, it has been previously required to use an additional diode for compensating for a voltage due to the negative temperature coefficient of the forward voltage drop across the diode in the "OR" circuit.
Accordingly, it is an object of the present invention to provide a new and improved generator's output control device decreased in the influence of a temperature.